1. Field of the Invention
This invention relates to a polymer blend comprising an aromatic polyester composition and polyglycolic acid. The polyester composition according to the invention comprises sulfo-modified copolyester. This blend can be formed into articles that have improved gas barrier and good clarity. The invention also relates to various methods of making the blend, including using master batch processes. Additionally, the present invention also contemplates a method of making a preform or container from the blend.
2. Prior Art
In recent years, much activity and invention in the art of polyesters has centered on the development of articles made from polyethylene terephthalate (PET). Containers and films constructed of PET have found wide acceptance in the packaging of food stuffs, medicines, consumer products and in particular carbonated soft drinks.
As longer shelf lives are required and smaller carbonated soft drink containers are being used, PET requires an improvement in gas barrier properties, especially an improvement in carbon dioxide permeability.
One approach has been the use of multilayer bottles containing a layer of a high barrier polymer such as an ethylene-vinyl-alcohol copolymer (EVOH), partially aromatic polyamide, or the like. U.S. Pat. No. 6,673,403 discloses a multilayer container using polyglycolic acid as the barrier layer. U.S. Pat. No. 4,424,242 also discloses a multilayer packaging material using polyglycolic acid as a barrier layer between layers of PET.
U.S. Pat. No. 4,565,851 discloses a blend of 5 to 50% by weight polyglycolic acid and 50 to 95% by weight of PET. However it has been found that these blends form a hazy article.
US Pat. Application No. 2006/0100392 also discloses polyglycolic copolyesters with a minor amount of aromatic polyester resins, preferably 30%.
U.S. Pat. No. 4,729,927 discloses a blend of PET and a copolymer comprising 40 to 95 mole % of ethylene isophthalate units and 5 to 60 mole % polyglycolic acid units. There is no information on the haziness of the bottle.
U.S. Pat. No. 6,309,718 relates to large containers, greater than 200 grams, that contain from 6 to 17 mol. % isophthalic acid. There is no disclosure relating to a blend of this copolyester with polyglycolic acid or a solution to the haze of the resulting blend.
EP 1 582 564 A1 discloses a copolyester of a hydroxy carboxylic acid and an aromatic dicarboxylic acid, exemplified by isophthalic acid, to be blended with a polyester resin. A specific molar ratio range of continuously bonded hydroxy carboxylic acid to isolated hydroxy carboxylic acid units is claimed which improves the transparency and gas permeability compared to the polyester resin.
There is a need for a simple blend of PET copolymer with a high barrier polymer, such as polyglycolic acid, that will give a clear monolayer article having improved gas barrier properties.